Frogs and Toads of Illinois
The American Bullfrog is the largest native frog in the United States. There is no dorsal ridge that runs down its back on the American Bullfrog. This is the distinguishable characteristics of the frog.
The Green Frog looks very much like the American Bullfrog but it’s a tad smaller. It has a dorsal ridge that runs down its back but they are incomplete and do not reach all the way.
The Wood Frog (Lithobates sylvaticus) is one of the most widespread frog in the United States but it’s a little rare in Illinois. It’s listed by the states as a Species in Greatest Need of Conservation. It’s fairly easy to distingush because of it’s mask around it’s eyes.
The Crawfish Frog gets its name from living in crawfish holes. Its has skin folds on the side and a small typanum. It also has a pair of vocal sacs for calling.
The Southern Leopard Frog has a white spot on its tympanum which can help differentiate the species from the other two. The Plains Leopard Frog is different from the Southern and Northern Leopard Frog because of its dorsal ridge. The Plains Leopard Frogs has a break and an indent near its butt while the North and South Leopard Frog just has a straight line.
Pickeral Frog looks like the leopard frogs but its spots are more rectangular than the leopard frogs.
Cricket Frogs – Acris
The Northern Cricket Frog is the only cricket frog in the state. Its skin is relatively more rough than the other tree frogs in the state. It also has no distinct markings.
Tree Frogs – Hyla
These two frogs are identical besides their calls and chromosome numbers. Note that Gray Tree Frogs are not always gray and can be green. They have yellow or orange coloration on their back legs which is nice to identify them.
The Cope’s Gray Tree Frog, the Eastern Gray Tree Frog and the Bird-Voiced Frog look very much a like. The difference is the coloration on the inner thigh. Cope’s Gray Tree Frog and Gray Tree Frog has brighter orange color on the thigh while the Bird-Voiced Frog is more greenish-yellow.
The Green Tree Frog does not have any coloration on its inner legs. It has a white line that runs down its side.
Chorus Frogs – Pseudacris
The Spring Peeper is a notoriously loud frog and one of the first signs of spring. It has a noticeable X marking on its back.
The Boreal Chorus Frog is found throughout the state besides the southern tip. The middle stripe on its back is occasionally broken. It also has really small legs.
The Midland or Western Chorus Frog is found in the Southern half of the state. The three stripes on its back are rarely broken.
The Upland Chorus Frog is found on the southern tip of the state. The stripes on it’s back are often broken up and can appear as spots.
The Illinois Chorus Frog does not have a white line that extends off the lips while the other chorus frogs do.
The family Bufonidae is known for the toxins / poison they produce called Bufotoxins. It is a bad idea to try to eat these guys.
The American Toad and Fowler’s Toad look fairly similar. The Fowler’s Toad has their cranial crest and the parotoid gland touch while the American Toad’s cranial crest and parotoid gland do not touch or are connected by a spur. The American Toad has a more speckled belly while the Fowler’s Toad has a clear, white one.
The Eastern Spadefoot Toad is the only Spadefoot toad in the state so it can easily be identified because of the spade on its back legs.
The Eastern Narrow Mouthed Toad is the only narrow mouthed toad in the state. One could potentially misidentify it has a Spadefoot toad because of its burrowing lifestyle but the head is narrower and there’s no spade on the back feet.